This project aims to uncover signaling molecules that initiate heart formation in the early embryo and limit dorsal spread of heart tissue, and study the possible involvement of the Notch/Delta signalling interaction in limiting the size of the heart. Aim 1 is to co-culture regions of the blastula known by fate mapping to give rise to the heart together with the endoderm, which is known to induce heart, and use many markers of cardiac development to see what exactly has been induced. Aim 2 is to take the same cardiogenic regions and overexpress various growth factors artificially in adjacent cells, and ask whether this induces heart. Aim 3) is to co-culture the lateral and ventral mesoderm of the tailbud stage embryo together with isolated neural tissue, to see if less heart tissue forms. Aim 4) is to overexpress notch or a domininant-negative form of notch, by injection into blastomeres in the heart-forming region, and see if the amount of heart-forming tissue is altered.